In contrast to conventional tool material such as a cemented carbide tool, a sintered cBN compact tool has excellent chemical stability, and high material performance characteristics due to low affinity for iron and high hardness, the performance characteristics capable of achieving long life with high efficiency. In addition, the sintered cBN compact tool has excellent flexibility far superior to that of a grinding tool which is a plastic working tool such as a cutting tool. The sintered cBN compact tool also has a reputation for low environmental load, and thus a conventional tool has been replaced by the sintered cBN compact tool in machining hard-to-machine iron-based material.
On the other hand, a cemented carbide tool, which is normally used in machining an Ni-based heat resistant alloy or an iron-based heat resistant alloy, has a cutting speed of approximately 50 m/min and the cutting speed can be increased up to approximately 80 m/min at most. For this reason, high speed cutting of 200 m/min or higher is being studied, in which a sintered cBN compact tool having excellent high temperature hardness is used. However, the problem in the case where a heat resistant alloy is cut with a sintered cBN compact tool is that fracture occurs at a side cutting edge, and at present, the reliability of the tool is not sufficiently ensured.
In view of such a situation, as described in the below-mentioned PTL 1, an attempt is made in which heat generated at the edge is efficiently distributed over a workpiece side by reducing the thermal conductivity of a sintered cBN compact, and thus the hardness of the workpiece is decreased to improve machinability, thereby reducing boundary fracture of the side cutting edge.
In addition, as described in the below-mentioned NPL 1 and PTL 2, adhesion resistance is attempted to be improved by forming a fine bumpy structure on the tool surface as a contrivance in the shape.
Furthermore, in NPL 2, chip flow is attempted to be controlled by forming a flute of 0.05 mm on the rake face of the tool. However, even with the contrivance in the shape like the above, it was not possible to achieve reduction in fracture of the side cutting edge of a sintered cBN compact tool in machining a heat resistant alloy.